Abstract:

Large flowers often contain larger nectar rewards, and receive more pollinator visits, than small flowers. We studied possible behavioral mechanisms underlying the formation of flower size preferences in bumblebees, using a two-phase laboratory experiment. Experimentally naive Bombus terrestris (L.) foraged on artificial flowers that bore either a big (3.8cm diameter) or a small (2.7cm diameter) display of a uniform color. Only flowers of one display size contained nectar rewards. We changed the display color and the locations of big and small flowers in the second experiment phase. We recorded the bees' choices in both phases. Almost one half of the bees (41) made their first visit to a small flower. The bees learned to associate display size with food reward, and chose rewarding flowers with >85 accuracy by the end of each experimental phase. Some learning occurred within the bees' first three flower visits. Learning of the size-reward association was equally good for big and small displays in the first experimental phase, but better for small displays in the second phase. Formation of size-reward associations followed a similar course in both phases. This suggests that the bees did not apply their experience from the first learning phase to the new situation of the second phase. Rather, they treated each phase of the experiment as an independent learning task. Our results suggest that associative learning is involved in the formation of preferences for large displays by bees. Moreover, bees that had learned to prefer large displays in one foraging situation may not transfer this preference to a novel situation that is sufficiently different. We propose that this feature of the bees' behavior can select for honest advertising in flowers.

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